View Full Version : Is WiFi a potential flight safety problem?

10th May 2003, 17:52
I have just discovered that my new laptop will have a thing called a 'Wireless Mini-PCI Card' fitted. This contains a small 2.4GHz radio transmitter with a range of over 1000ft.

We know that GSM apparently causes problems and the cabin staff always remind passengers to turn off their phones - but with the advent of laptops with embedded WiFi transceivers, is there another flight safety problem looming? Presumably the card can be controlled by software to stop it functioning in an aeroplane cabin - or does it stay in a safe quiescent mode until it sniffs out a local access point?

Another computer in aeroplane safety issue - why are 'computers with CD-ROM drives' not allowed to be used in flight (certainly on LH)? With most new laptops now coming with DVD/CD-RW drives fitted and Joe Punter keen to watch a DVD, is there really a legitimate safety issue here?

Sorry if this is the wrong site for this post, so please move it as appropriate. But it was news to me that quite a few passenger laptops contain 2.4 GHz transceivers nowadays!

10th May 2003, 18:27
the default behaviour on my Toshiba laptop is that the wireless adapter continously searches for available wireless networks. I would have to manually set the software to stop the transmission.

Maybe some of the more-techie minded people could explain whether this is an on-board hazard? FWIW, since buying a GameBoy Advance I rarely use my laptop during flights any more :D

10th May 2003, 19:05
<<the default behaviour on my Toshiba laptop is that the wireless adapter continously searches for available wireless networks. I would have to manually set the software to stop the transmission.>>
I think what you are saying may contradict itself...

<<continously searches for available wireless networks.>>
I suspect this is by "listening" for any available transmissions?

<<to stop the transmission>>
I would have thought it would only "transmit" when it has detected a network to transmit to....??

I have just checked my mobile phone, which when "transmitting" interferes with my PC sound system (in the same way it interferes with airliner R/T in the "theoretical" case of my forgetting to turn it off!). The mobile did not transmit while it was "searching" for a Network. The moment it detected BT Cellnet, it started transmitting...

So long as there is no wireless network detected I would have thought all was OK. That said, is not "connexion by Boeing" (or whatever they call it?) wireless using this system?? I think I saw somewhere that it was, but the transmission power was much lower than a mobile... and therefore OK? Although again, I've just a PC Mag article showing you to contruct some DIY aerial that increases the transmission power (?) / range easily.

CD-ROMs - there was a problem with some CD-ROMs emitting some RF that caused interference, hence LH's rule. As you say, pretty impractical to enforce it now...

10th May 2003, 19:56
The short answer is: No One Knows! The topic is touched on the later parts of the thread "Mobile Phones ... CAA" running in Rumours & News.

As I understand it, Connexion by Boeing does use wifi but the power levels are considerably lower than for a mobile phone. Manufacturers should have placed an easy hardware or software button to disable this feature but may not have done. If the software off-switch is through a couple of menu's try placing a shortcut to it on the desktop and turning it off before leaving for the airport, or whilst in the lounge.

'Bluetooth' is a another short range radio system used ofr mobiles, PCs and PDAs (amongst other things). This should also be turned off as no one yet knows how problematic it can be. (I sit to be corrected on this point)

"Radios that comply with the Bluetooth wireless specification operate in the unlicensed, 2.4 GHz radio spectrum ensuring communication compatibility worldwide. These radios use a spread spectrum, frequency hopping, full-duplex signal at up to 1600 hops/sec. The signal hops among 79 frequencies at 1 MHz intervals to give a high degree of interference immunity."

We are at the beginning of investigating and regulating the problem of RF generated by Pax held devices.

10th May 2003, 20:04
The airline I work for has recently introduced laptops in the flightdeck. In order to gain CAA approval for this the WiFi transmitter has to be disabled during the flight. Our systems department have found a way to do this and so whilst no one really knows what the effects might be, the answer is as far as the CAA are concerned - NO, the WiFi transmitter must be disabled before flight. If you cannot do this then the laptop must not be used.

The general rule is that anything which has the capability to transmit on a radio frequency is banned - this is why Furbees were not allowed a few years back.


10th May 2003, 20:14
I always turn the Bluetooth transmitter off on my PDA when flying. Saves battery life as well!

Wi-Fi is very low power compared to mobiles, and indeed is used on the Connexxion system: http://www.80211-planet.com/news/article.php/1570531

The interesting thing is the weight factor of Ethernet cables compared to wireless, and also the cost of installation. I wonder if 802.11g (the fastest WiFi available) could be used in future to transmit TV/audio signals, negating the need for complex IFE installations?

10th May 2003, 20:17
I think Paxboy is correct - the sort answer is no one really knows.

My understanding is WiFi and Bluetooth use the same frequency range (2.4Ghz) but with different power levels, hence Bluetooth has a nominal range of around 10m whilst WiFi is allegedly up to around 300m.

Mobile phones tend to have a range much higher than this and hence transmit at a higher power - also there is a problem for the mobile phone networks as the whole principle is based upon the phone only seeing one or two basestations - when it is at several thousand feet it can see a lot more and the network can get horribly confused.

Also I had heard in the past that some mobile phone frequencies are very close to aircraft navigation frequencies - I really ought to know this - typically 900Mhz. The only thing I could think of for this would be a localiser - perhaps someone could correct me?

I think connexion does use WiFi - the LH trial is using approved laptops but I read somewhere that you would be able to get your own laptop "approved" for use on the system in the future which would suggest it is using normal WiFi?

Very confusing!


11th May 2003, 02:24
NigelOnDraft, the adaptors acutally register by sending, WiFi networks don't send out 'pings' to find adapters. So 'searching for networks' actually means the adaptor is transmitting.

11th May 2003, 03:31
my sony vaio notebook has a hardware switch to disable wireless lan

Grilled Tomato
11th May 2003, 03:36
https://www.bluetooth.org/foundry/sitecontent/document/whitepapers_presentations is a useful link on the Bluetooth special interest group's website.

One other factor is that both Bluetooth and WiFi frequency hop (unlike basic GSM / GPRS), ensuring they are tolerant to interference, and also interfere less on any particular frequency within the operating band.

Bluetooth has three power classes 1mW, 2.5mW and 100mW, giving nominal ranges of 10m, 20m and 100m (although three times that can be achieved with good receivers). Compare that to GSM which potentially can be used to 35Km, or even 120Km on extended range, take into account the inverse square law for propagation, and you get some idea of the power comparisons.

Hope this helps.

Final 3 Greens
11th May 2003, 05:23
LIfe Alfboy, my Sony has a switch to disable wifi.

As I fly a lot, I check it is 'off' before every flight.

There may be more of a problem with all the new combined PDA/phones that are hitting the market - let's hope the punter disable radio freq.

However, these are (mainly) the same users who never listen to the safety brief etc.......

11th May 2003, 10:16
GSM phones operate in 2 frequency bands in Europe - 900MHz & 1800MHz. In North America a 1900MHz band is used for GSM networks. And frequency hop, but not during a call.

GSM phones also modulate the amount of power used for transmission. This improves battery life and gives the base station a chance of handling signals from a few metres away to signals from kilometres away.

The base station aerial design makes most of the signal travel in a roughly horizontal direction. Which means at 30,000feet if a phone did find a base station, it would probably transmit at it's max power (only 8watts I believe for handsets). The phone, basestation and network would have no problem whatsoever in maintaining contact.

I predict within a few years, airlines will introduce phone access on aircraft. Probably not GSM, but maybe 3G networks if they work with manufacturers to certify the equipment. Allowing people to use their own phones on a long flight would be a nice little earner.

All the best

Iron City
14th May 2003, 00:07
Understand the Lufthansa airplanes cost $500,000 a go to equip. Wonder if they will make it back anytime soon.

The WiFi and any other RF floating around an aircraft can cause problems, the problem seems to be it is different for different emitters and different aircraft. The CAA work is a good start, but until more is known about the low power, pulse freq. hopping xmitters and their interaction with different types of equipment it is a ll trrial and error.

4th Jun 2003, 23:54
802.11b equipment operates in 2.4 GHz with up to 13 different channels (frequencies), but not all of them are allowed worldwide. As it's already been said, it's an unlicenced band that can be freely used as long as emitted power does not exceed 100mW.

Average Wi-Fi equipment uses 30-50 mW of output power.

Re: 802.11g. It's not the fastest wireless available. It operates in the same 2.4 GHz band as 802.11b, and it should be capable of providing 20 Mbps. However, this figure drops dramatically when 802.11b client associates with a 802.11g access point, because the standard mandates that in this case some of the bandwidth must be allocated to slower client to "catch-up". The fastest wireless is 802.11a, which offers true 54 Mbps (not only declared one like 802.11g), but since it operates on 5 GHz band, the range is very very low.

Back on topic: IANAP (I am not a pilot), but I would consider any Wi-Fi equipment as a threat to filght safety.

5th Jun 2003, 04:36
I agree - threat not assessed = threat not disproven.

Have now got to grips with the new toy; both the 2.4GHz WiFi system and the tri-GSM band Vodafone GPRS PC card can be turned off at the system tray. That's what I'll do when I fly; but how many others will be bothered to....??

5th Jun 2003, 06:34
My Toshiba laptop has a mechanical switch on the front that switches the WiFi & Bluetooth antennas on/off.

7th Jun 2003, 03:24
Nobody else has brought this up so I will.
Did you ever wonder how a cop knows you're using a radar detector even if it's hidden?
Every electronic component, even a receiver, transmits. Not much but it is measurable. The cop has a detector to pick up the internal amplifier emmissions from the detector.
AM radios used to be notorious for emitting IF radiation which would mess up other radios in the area and was very easy to detect.
In parts of Europe if you didn't pay your TV tax there are vehicles that cruise neighborhoods to see if there are TV's operating in homes where the tax hasn't been paid. They're detecting that emission put out by the TV's.

What I'm leading up to is any electronic component is capable of causing interference with any other component operating on a frequency close to one being emitted.
All amplifiers emit radiation. All data busses require amplification. Computers use data busses to transfer data internally. The processor may be in the 1 or 2 GHz speed range but the data bus probably is operating on a frequency of about 100 to 150 MHz. That has nothing to do with speed. It's the frequency of the bus. Like a radio station frequency. They are equivalent to an AM radio station. The new cell phones are actuall mini computers with internal data busses, with comparitively strong transmitters, and all that implies.

So what you have with a computer is an AM radio station transmitting on a frequency of somewhere near 100 to 150MHz.
VOR and ILS happens to operate on AM in that frequency range. Draw your own conclusions, It's already caused three documented incidents and two missed approaches and been demonstrated to cause localizer deviataions up to 3 degrees by the US Air Force at Wright Pat and NASA.

Turn off the Stinking Status Symbols on takeoff and approach!

I'm done typing.

7th Jun 2003, 03:39
....and some years ago a TV reporter drove around London and demonstrated how to read your computer screen while sitting outside your office in a van.

7th Jun 2003, 19:58
There's a lot of muddled 'information' being played in this thread and elsewhere on prrune about radio emissions,

1) Different devices and and different bandwidths have to be considered seperately. The "it's all really scary" idea is an unhelpful nonsense.

2) The signals emitted by CRTs and associated HT gear in televisions is not relevant. Passengers do not bring televisions on to aircraft.

3) With respect to WiFi, "noone really knows" is quite a sweeping statement to present as fact. Lufthansa, their aircrew et al obviously think they do know reasonably well enough.

4) The power levels for WiFi are considerably lower than for mobiles, and this is part of the general standard, not an aviation specific implementation.

5) There are often quoted 'document incidents' in these discussions. It would help credibility if URLs were posted, i.e. to the relevant NTSB/AAIB reports or whatever.

10th Jun 2003, 04:09
Here's two links.
Paulo, different bandwidths do, indeed, have to be considered separately. The problem is they all generate harmonics capable of interferring with all bandwidths.
In the last two months there have been at least four published reports concerning Interference caused by PED's and Cell Phones.
With the GPS signal being weak enough to require an antenna installed Op Amp so the signal is usable at the receiver sensor I wonder that anyone would question the possibility of passenger induced interference or want to argue turning the devices off at least on approach.
Heaven forbid we should interfere with the rights of a movie viewing, laptop game playing, or last minute rental car arranging passenger in the interests of flight safety.
Hey, let's bring back free-for-all smoking flights. It does make the pressurization leaks easier to find from the outside.


If you have a subscription to AIR SAFETY WEEK here's a bunch more:

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11th Jun 2003, 08:59
Yes, let's definitely look at the CAA report.

Should the passenger ban continue? For sure. But read the document - read the nature of the test, the proximity to the avionics - if the text is too hard, look at the photo in Appendix 8

What they were simulating was the active use of mobiles in the cockpit, not Mrs Jones in row 10 who's forgotten to turn her phone off. The idea that this is just a passenger issue isn't true, and it isn't the CAA's conclusion either. (See section 7 'Recommendations')

11th Jun 2003, 13:55
No matter what theories one can produce or what anyone thinks is safe, under FARs and JARs it is an offence for anyone to use or permit to be used, any device that intentionally emits electromagnetic radiation in an aircraft, at any time, unless the device has been proven not to cause interference with the aircraft systems. The regulations don't say how much radiation or what frequency, they categorically cover ALL transmitting devices that haven't been specifically tested. There are perfectly good reasons for the rules, based on testing carried out by the RTCA on behalf of ICAO and the FAA.

The laptops used on Lufthansa's Connexion demonstration flights were all tested and found not to affect the aircraft systems. LH propose to lend PCs to people who wish to use the service. Eventually control standards will be introduced to permit general use of Wi-Fi equipment on aircraft. Until then it remains unlawful to use any transmitting device unless it has been proven not to interfere with the aircraft systems. Bring your certificate.

Through difficulties to the cinema

12th Jun 2003, 10:29
In the paper today, two airlines announced plans for wi-fi inflight capability in the very near future. I have misplaced the article and forgotten the names. I believe they were US carriers. My guess, in two years, nearly everyone will have it.


12th Jun 2003, 22:29
I doubt there's anything special about the Lufthansa setup. It's off the shelf Cisco Aironets for the routing, and something equally off the shelf at the laptop end I'd expect. There are people who'd argue that the CAT5 part of the setup is worse for emissions.

I guess one could have manufacturers who didn't follow the power or frequency standards (lets say Acme Inc. sell 'WifiMegaBooster') so then there in that case there is an untested scenario.

Arguably if you were close enough to the avionics, and you boost say 20x, you'd now be in the same territory as the CAA tests on mobiles. (with Mag comp. deflections, VOR swing, that kind of stuff)

12th Jun 2003, 23:44
(I'm coming at this from a hypothetical "is it safe".

Most times I fly I am expressly permitted by the FAA regulations mentioned above to make the judgement myself, but I'm not really interested in having a laptop hit me on the head in the middle of a roll ;)